Many homeless people in the US have poorly treated or untreated mental illnesses.Credit:Bloomberg

Damian Ferrie, chair of Mental Health Victoria, said that Victoria was already showing the signs of following the path of US cities such as Los Angeles and San Francisco, where untreated mental illness spills out onto the streets in large homeless populations.

Mr Ferrie said this was reflected in the numbers of young people locally who were now living on the streets or without a stable home (an estimated 43,500 people under 25 are homeless Australia-wide).

"Homelessness is no longer that perception of old drunk men with bottles of port. These are young people," he said.

Experts say a key problem is a shortage of psychiatric and other mental health support services for people before they become acutely ill. Without them, they are getting worse and turning up in crisis to emergency departments.

Associate Professor Richard Newton from the Royal Australian and New Zealand College of Psychiatrists said this dearth of appropriate services meant people with worsening mental health conditions were getting the message that they were "not sick enough" for help.

"If it's apparent you’re not (at risk of killing yourself), then it feels like any offer of services is withdrawn and you are recommended to go back to your GP," he said.

Staff working within acute mental health facilities are also under increasing pressure because it’s common for nurses, psychiatrists and other staff to be subjected to violence, Professor Newton said.

"We have all been either physically assaulted or terrified by a threat to our safety on numerous occasions over and over again."

The report calls for an additional $543 million in mental health support in Victoria, including $200 million a year for community mental health services and $65 million for 204 acute hospital beds.

Premier Daniel Andrews indicated he could be willing to dig deeper on mental health funding in a speech to the Victorian Council of Social Service on Wednesday.

He highlighted the state's "staggering" suicide rate (624 in Victoria in 2016) and said as important as the $705 million budget commitment was "we all know that there is so much more we need to do in this space".

Dr Tony Bartone, a GP and president of the Australian Medical Association, said the only way he could get immediate mental health help for his patients was if they were at imminent risk of harming themselves.

"I practice in the north west suburbs of Melbourne... a stone’s throw from three major teaching hospitals, but I don’t have access to any public emergency facilities," he said.